Abstract: The past few years have witnessed increased interest in the potential use of wireless sensor networks (WSNs) in applications such as disaster management, combat field reconnaissance, border protection and security surveillance. Sensors in these applications are expected to be remotely deployed in large numbers and to operate autonomously in unattended environments. To support scalability, nodes are often grouped into disjoint and mostly non-overlapping clusters. In this paper, we present a taxonomy and general classification of published clustering schemes. We survey different clustering algorithms for WSNs; highlighting their objectives, features, complexity, etc. We also compare of these clustering algorithms based on metrics such as convergence rate, cluster stability, cluster overlapping, location-awareness and support for node mobility.

Abstract: Wireless sensor network (WSN) is a wireless ad hoc network that consists of very large number of tiny sensor nodes communicating with each other with limited power and memory constrain. WSN demands real-time forwarding which means messages in the network are delivered according to their end-to-end deadlines (packet lifetime). This paper proposes a novel real-time routing protocol with load distribution (RTLD) that ensures high packet throughput with minimized packet overhead and prolongs the lifetime of WSN. The routing depends on optimal forwarding decision that takes into account of the link quality, packet delay time and the remaining power of next hop sensor nodes. The proposed mechanism has been successfully studied and verified through simulation and real test bed implementation.

Abstract: Enterprises are increasingly deploying Wireless LANs to provide mobile access to users in corporate offices. However, existing enterpriseWLANs are far from being truly mobile. In particular, they do not adequately support continuous mobility, where users access the network on-the-go. Furthermore, WLANs that do provide continuous mobility support require client modifications, making them hard to deploy in practice 20. In addition, with the growing interest in realtime applications such as voice and video, users are increasingly placing additional (QoS) demands on the network, which for inadequately designed WLANs, does not scale to large numbers of users 10. In this paper, we propose Overcast, a novel WLAN architecture that targets scenarios demanding continuous mobility and real-time support for 802.11 clients. Overcast does not require client modifications and supports all 802.11 standards. Though Overcast borrows some features from priorWLAN designs, it improves on them by incorporating a novel RF mapping framework (proposed in 3) for accurate online detection of RF interference. We describe the architecture of Overcast in detail and discuss our current efforts in realizing such a system on off-the-shelf commodity hardware. We also describe an example application of Overcast to highlight it’s usefulness in supporting realtime applications in continuously mobile user environments.

Abstract: The availability of low-cost hardware such as CMOS cameras and microphones has fostered the development of Wireless Multimedia Sensor Networks (WMSNs), i.e., networks of wirelessly interconnected devices that are able to ubiquitously retrieve multimedia content such as video and audio streams, still images, and scalar sensor data from the environment. In this paper, the state of the art in algorithms, protocols, and hardware for wireless multimedia sensor networks is surveyed, and open research issues are discussed in detail. Architectures for WMSNs are explored, along with their advantages and drawbacks. Currently off-the-shelf hardware as well as available research prototypes for WMSNs are listed and classified. Existing solutions and open research issues at the application, transport, network, link, and physical layers of the communication protocol stack are investigated, along with possible cross-layer synergies and optimizations.

Abstract: The advancement in wireless communications and electronics has enabled the development of low-cost sensor networks. The sensor networks can be used for various application areas (e.g., health, military, home). For different application areas, there are different technical issues that researchers are currently resolving. The current state of the art of sensor networks is captured in this article, where solutions are discussed under their related protocol stack layer sections. This article also points out the open research issues and intends to spark new interests and developments in this field.

Abstract: This paper describes the concept of sensornetwrRN wtw has been made viable by the convergence of microelectro -mechanical systems technology,wechnol communications and digital electronics. First, the sensing tasks and the potential sensornetwRVB applications are explored, and areview of factors influencing the design of sensornetwrR( is provided. Then, the communication architecture for sensornetwrRN is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor network are also discussed.

Abstract: Wireless sensor networks consist of small nodes with sensing, computation, and wireless communications capabilities. Many routing, power management, and data dissemination protocols have been specifically designed for WSNs where energy awareness is an essential design issue. Routing protocols in WSNs might differ depending on the application and network architecture. In this article we present a survey of state-of-the-art routing techniques in WSNs. We first outline the design challenges for routing protocols in WSNs followed by a comprehensive survey of routing techniques. Overall, the routing techniques are classified into three categories based on the underlying network structure: flit, hierarchical, and location-based routing. Furthermore, these protocols can be classified into multipath-based, query-based, negotiation-based, QoS-based, and coherent-based depending on the protocol operation. We study the design trade-offs between energy and communication overhead savings in every routing paradigm. We also highlight the advantages and performance issues of each routing technique. The article concludes with possible future research areas.

Abstract: Energy conservation techniques for sensor networks typically rely on the assumption that data sensing and processing consume considerable less energy than communication. This assumption does not hold in some practical application scenarios, where ad hoc developed sensor units require power consumption comparable with, or even larger than, that of the radio. In this paper we focus on an embedded sensor for monitoring snow composition in mountain slopes for avalanche forecasting. To lower the sensor energy consumption we propose an adaptive sampling algorithm able to dynamically estimate the optimal sampling frequency of the signal to be monitored. In turn, this minimizes the activity of both the sensor and the radio (hence saving energy) while maintaining an acceptable accuracy on the acquired data. Simulation experiments show that the suggested solution can save up to 97% of the energy consumed for sensing when the sensor is always on, while maintaining the error at acceptable levels.

Abstract: Wireless Sensor Networks are without a doubt one of the central issues in current research topics due to the harsh environmental conditions in which such networks can be deployed and their unique sensor network characteristics,specifically limited power supply, sensing, processing and communication capabilities. Presented with many challenges and design issues that affect the data routing, a need for a fault tolerant routing protocol becomes essential. In this paper, we summarize and highlight the key ideas of existing fault tolerant techniques of routing protocols, survey existing routing protocols proposed to support fault tolerance. Finally, we provide some future research directions in the area of fault tolerance in wireless sensor networks routing.

Abstract: Several sensor network applications based on data diffusion and data management can determine the communication transfer rate between two sensors beforehand. In this framework, we consider the problem of energy efficient communication among nodes of a wireless sensor network and propose an application-driven approach that minimizes radio activity intervals and prolongs network lifetime. On the basis of possible communication delays we estimate packet arrival intervals at any intermediate hop of a fixed-rate data path. We study a generic strategy of radio activity minimization wherein each node maintains the radio switched on just in the expected packet arrival intervals and guarantees low communication latency. We define a probabilistic model that allows the evaluation of the packet loss probability that results from the reduced radio activity. The model can be used to optimally choose the radio activity intervals that achieve a certain probability of successful packet delivery for a specific radio activity strategy. Relying on the probabilistic model we also define a cost model that estimates the energy consumption of the proposed strategies, under specific settings. We propose three specific strategies and numerically evaluate the associated costs. We finally validate our work with a simulation made with TOSSIM (the Berkeley motes' simulator). The simulation results confirm the validity of the approach and the accuracy of the analytic models.

Abstract: In the last years, wireless sensor networks (WSNs) have gained increasing attention from both the research community and actual users. As sensor nodes are generally battery-powered devices, the critical aspects to face concern how to reduce the energy consumption of nodes, so that the network lifetime can be extended to reasonable times. In this paper we first break down the energy consumption for the components of a typical sensor node, and discuss the main directions to energy conservation in WSNs. Then, we present a systematic and comprehensive taxonomy of the energy conservation schemes, which are subsequently discussed in depth. Special attention has been devoted to promising solutions which have not yet obtained a wide attention in the literature, such as techniques for energy efficient data acquisition. Finally we conclude the paper with insights for research directions about energy conservation in WSNs.

Abstract: This paper reports the experimental and analytical results of a two-story reinforced concrete frame instrumented with innovative piezoceramic-based smart aggregates (SAs) and subjected to a monotonic lateral load up to failure. A finite element model of the frame is developed and analyzed using a computer program called Open system for earthquake engineering simulation (OpenSees). The finite element analysis (FEA) is used to predict the load–deformation curve as well as the development of plastic hinges in the frame. The load–deformation curve predicted from FEA matched well with the experimental results. The sequence of development of plastic hinges in the frame is also studied from the FEA results. The locations of the plastic hinges, as obtained from the analysis, were similar to those observed during the experiment. An SA-based approach is also proposed to evaluate the health status of the concrete frame and identify the development of plastic hinges during the loading procedure. The results of the FEA are used to validate the SA-based approach for detecting the locations and occurrence of the plastic hinges leading to the progressive collapse of the frame. The locations and sequential development of the plastic hinges obtained from the SA-based approach corresponds well with the FEA results. The proposed SA-based approach, thus validated using FEA and experimental results, has a great potential to be applied in the health monitoring of large-scale civil infrastructures.

Abstract: Wireless sensor networks are an emerging technology for low-cost, unattended monitoring of a wide range of environments. Their importance has been enforced by the recent delivery of the IEEE 802.15.4 standard for the physical and MAC layers and the forthcoming ZigBee standard for the network and application layers. The fast progress of research on energy efficiency, networking, data management and security in wireless sensor networks, and the need to compare with the solutions adopted in the standards motivates the need for a survey on this field.

Abstract: This tutorial paper examines architectural and circuit design techniques for a microsensor node operating at power levels low enough to enable the use of an energy harvesting source. These requirements place demands on all levels of the design. We propose an architecture for achieving the required ultra-low energy operation and discuss the circuit techniques necessary to implement the system. Dedicated hardware implementations improve the efficiency for specific functionality, and modular partitioning permits fine-grained optimization and power-gating. We describe modeling and operating at the minimum energy point in the subthreshold region for digital circuits. We also examine approaches for improving the energy efficiency of analog components like the transmitter and the ADC. A microsensor node using the techniques we describe can function in an energy-harvesting scenario.

Abstract: The deployment of wireless applications or protocols in the context of Mobile Ad-hoc NETworks (MANETs), often requires to step through a simulation phase. For the results of the simulation to be meaningful, it is important that the model on which is based the simulator matches as closely as possible the reality. In this paper we present the simulation results of a straightforward algorithm using several popular simulators (OPNET Modeler, NS-2, GloMoSim). The results tend to show that significant divergences exist between the simulators. This can be explained partly by the mismatching of the modelisation of each simulator and also by the different levels of detail provided to implement and configure the simulated scenarios.

Abstract: IEEE 802.15.4 is a new standard uniquely designed for low-rate wireless sensor networks (WSNs). It targets low data rate, low power consumption and low-cost wireless networking, and offers device level wireless connectivity. The purpose of this paper is to propose a traffic adaptive power control algorithm for beacon relayed distributed WSNs.

Abstract: Automated impact detection and characterization on aircraft and spacecraft has been an elusive goal due to the transitory nature of the detectable high-frequency signals involved. Invocon, Inc. has been awarded a NASA Phase 2 Small Business Innovation Research (SBIR) program to develop self-contained, miniaturized, piezoelectric sensory nodes with extremely low-power trigger modes that are synchronized within a radio frequency network. Each node will continuously monitor an accelerometer, acoustic emission sensor, or PZT element for an impact event, such as a micro-meteor impact or the foam impact that caused the Columbia tragedy. When a programmable threshold is exceeded, a low-latency signal acquisition circuit will capture the event as a digital waveform for post-processing and impact characterization including amplitude and time-of-arrival analysis. The innovative signal conditioning circuit design is capable of operation in the micro-watt range on average while constantly maintaining the capability to acquire and process very high frequency acoustic signals. Such performance can potentially provide operating lifetimes of 5 years on a single AA battery, or unlimited operation from scavenged power sources. Additionally, the system will provide a general purpose hardware platform on which Integrated Structural Health Monitoring (ISHM) algorithms and sensing techniques can be implemented. The same basic system design, with configurable sample rates, sensor interfaces, actuation outputs, and local processing algorithms, could be used for active or passive damage detection, locating leaks from pressurized vehicles and habitats through the produced airborne and surface-borne ultrasonic energy, or detecting crack propagation or delamination in structures through Acoustic Emission (AE) techniques. By allowing the development, demonstration, and potentially deployment of these ISHM capabilities on miniaturized devices optimized for low-power and distributed operation, th- e goals of ISHM will be more effectively achieved for aircraft and spacecraft. This paper shall provide a general description of the triggering capabilities, data acquisition circuit design, overall system design, and potential applications.

Abstract: In this paper, we study a cellular mobile communications network with multiple cells and multiple classes of calls. The different classes of calls have different call holding times and residence time distributions. We consider a protocol mechanism under which a blocked call in a cell is either disconnected from the network or is deemed as a handoff call in a neighboring cell. Under this protocol, we prove that the stationary distribution of this cellular mobile network has a product form. This allows us to derive explicit expressions for handoff rates of each class of calls from one cell to another and the disconnecting probabilities for each class of new and handoff calls. Our numerical results show how these measures depend on the mobility of the mobile terminals in each cell and on the numbers of reserved channels.

Abstract: In this paper, we assess the state of the art of Quality of Services (QoS) support in wireless sensor networks (WSNs). Unlike traditional end-to-end multimedia applications, many non-end-to-end mission-critical applications envisioned for WSNs have brought forward new QoS requirements on the network. Further, unique characteristics of WSNs, such as extremely resource-constrained sensors, large-scale random deployment, and novel data-centric communication protocols, pose unprecedented challenges in the area of QoS support in WSNs. Thus, we first review the techniques for QoS support in traditional networks, analyze new QoS requirements in WSNs from a wide variety of applications classified by data delivery models, and propose some non-end-to-end collective QoS parameters. Next, the challenges of QoS support in this new paradigm are presented. Finally, we comment on current research efforts and identify many exciting open issues in order to stimulate more research interest in this largely unexplored area.

Abstract: We present a number of performance studies of the IEEE 802.15.4 protocol. We put a special focus on application scenarios in industrial sensor network applications, which is one of the intended application domains for this protocol. The primary requirements are reduced end-to-end latency and energy consumption. Our studies are based on our new implementation of IEEE 802.15.4 developed for the simulation framework OMNeT++. We performed extensive simulations that demonstrate the capabilities of this protocol in the selected scenarios but also the limitations. In particular, we investigated the dependency of the protocol on protocol-inherent parameters such as the beacon order and the superframe order but also to different traffic load. Our results can be used for planning and deploying IEEE 802.15.4 based sensor networks with specific performance demands.

Abstract: The IEEE 802.15.4 protocol has become the primary solution for many low-rate wireless personal area network (LR-WPAN) applications. This is especially the case for industrial sensor network applications such as automation control. We contribute to the better understanding of the protocol behavior by presenting a set of results of simulation experiments. Our results outline the capabilities of this protocol in the selected scenarios but also the limitations. In particular, we investigated the dependency of the protocol on protocol-inherent parameters such as the beacon order and the superframe order but also to different traffic load. Our results can be used for planning and deploying IEEE 802.15.4- based sensor networks with specific performance demands. We put a special focus on application scenarios in industrial sensor network applications. The primary requirements are reduced end-to-end latency and energy consumption. Our studies are based on our new implementation of IEEE 802.15.4 developed for the simulation framework OMNeT++.

Abstract: Wireless sensor networks (WSNs) use small nodes with constrained capabilities to sense, collect, and disseminate information in many types of applications. As sensor networks become wide-spread, security issues become a central concern, especially in mission-critical tasks. In this paper, we identify the threats and vulnerabilities to WSNs and summarize the defense methods based on the networking protocol layer analysis first. Then we give a holistic overview of security issues. These issues are divided into seven categories: cryptography, key management, attack detections and preventions, secure routing, secure location security, secure data fusion, and other security issues. Along the way we analyze the advantages and disadvantages of current secure schemes in each category. In addition, we also summarize the techniques and methods used in these categories, and point out the open research issues and directions in each area.

Abstract: Since wireless sensor networks contain large number of nodes, it is conceivable that nodes group together to perform tasks and form scale-free networks. The scale-free principles are evaluated with IEEE 802.15.4 MAC and ZigBee protocols. Two topologies, star and tree, are studied. Insights gained from the simulations show that orphaning affects the performance of the network, thus, compromising its resilience.

Abstract: Wireless sensor networks (WSNs) are being increasingly used in applications where low energy consumption and low cost are the overriding considerations. With increased use, their reliability, availability and serviceability need to be addressed from the outset. Conventional schemes of adding redundant nodes and incorporating reliability in control protocols can effectively improve only the reliability of the overall WSN. The availability and serviceability of WSN nodes can be addressed by providing the remote testing and repair infrastructure for the individual sensor nodes that is well matched with existing on-board test infrastructure, including standard JTAG chains. In this paper, we propose and evaluate scalable architectures of WSN nodes for increased availability as well as implement the proposed solutions using COTS components.

Abstract: Many wireless sensor network applications must resolve the inherent conflict between energy efficient communication and the need to achieve desired quality of service such as end-to-end communication delay. To address this challenge, we propose the real-time power-aware routing (RPAR) protocol, which achieves application-specified communication delays at low energy cost by dynamically adapting transmission power and routing decisions. RPAR features a power-aware forwarding policy and an efficient neighborhood manager that are optimized for resource-constrained wireless sensors. Moreover, RPAR addresses important practical issues in wireless sensor networks, including lossy links, scalability, and severe memory and bandwidth constraints. Simulations based on a realistic radio model of MICA2 motes show that RPAR significantly reduces the number of deadlines missed and energy consumption compared to existing real-time and energy-efficient routing protocols

Abstract: Software Defined Radio enables new protocols that are flexible and quick to deploy. Researchers can use the programmability of Software Radios to create tools that monitor and debug their work. In this paper, Open-source hardware and software is used to deploy a multi-channel monitoring tool of the IEEE 802.15.4 protocol.

Abstract: In this paper we present a first effort in assessing the reliability of OMNeT++ and the MAC Simulator framework insimulating Wireless Sensor Networks. A collection of metricson the flooding algorithm running on a simple testbed made of few Tmote Sky is used as reference to evaluate the qualityof the simulation results. Our experiments show that simulation results tend to over-estimate the metrics collected inthe testbed. A correcting factor derived from experimental evidences must be considered in order to improve the simulation results. At the best of our knowledge, this is thefirst result about the accuracy of OMNet++ in the wireless sensor network domain.

Abstract: This work introduces FAIR, a novel framework for Fuzzy-based Aggregation providing In-network Resilience for Wireless Sensor Networks (WSN). FAIR addresses the possibility of malicious aggregator nodes manipulating data. It provides data-integrity based on a trust level of the WSN response and it tolerates link or node failures. Compared to available solutions, it offers a general aggregation model and makes the trust level visible to the querier. We classify the proposed approach as complementary to protocols ensuring resilience against sensor leaf nodes providing faulty data. Thanks to our flexible resilient framework and due to the use of Fuzzy Inference Schemes, we achieve promising results within a short design cycle.

Abstract: In this paper we describe T-MAC, a contention-based Medium Access Control protocol for wireless sensor networks. Applications for these networks have some characteristics (low message rate, insensitivity to latency) that can be exploited to reduce energy consumption by introducing an activesleep duty cycle. To handle load variations in time and location T-MAC introduces an adaptive duty cycle in a novel way: by dynamically ending the active part of it. This reduces the amount of energy wasted on idle listening, in which nodes wait for potentially incoming messages, while still maintaining a reasonable throughput.We discuss the design of T-MAC, and provide a head-to-head comparison with classic CSMA (no duty cycle) and S-MAC (fixed duty cycle) through extensive simulations. Under homogeneous load, T-MAC and S-MAC achieve similar reductions in energy consumption (up to 98%) compared to CSMA. In a sample scenario with variable load, however, T-MAC outperforms S-MAC by a factor of 5. Preliminary energy-consumption measurements provide insight into the internal workings of the T-MAC protocol.

Abstract: Limited fidelity of simulators has prompted researchers to build wireless network testbeds for realistic testing. Unlike simulators, which have broad applicability, most of these testbeds are tailored to specific projects and cannot be used by a wider research community. Recognizing the growing importance of testbeds, this article is one of the first attempts to identify a comprehensive set of requirements for a general-purpose multihop wireless network testbed and the challenges therein. The issues range from initial testbed deployment and routine management to individual experimental configuration and data collection. We survey state-of-the-art wireless testbeds and highlight their salient features. The article is intended to provide an initial reference for researchers, application developers, and administrators dealing with various aspects of wireless network testbeds.

Abstract: Wireless sensor networks are appealing to researchers due to their wide range of application potential in areas such as target detection and tracking, environmental monitoring, industrial process monitoring, and tactical systems. However, low sensing ranges result in dense networks and thus it becomes necessary to achieve an efficient medium-access protocol subject to power constraints. Various medium-access control (MAC) protocols with different objectives have been proposed for wireless sensor networks. In this article, we first outline the sensor network properties that are crucial for the design of MAC layer protocols. Then, we describe several MAC protocols proposed for sensor networks, emphasizing their strengths and weaknesses. Finally, we point out open research issues with regard to MAC layer design.

Abstract: The IEEE 802.15.4 Low-Rate Wireless Personal Area Network (LR-WPAN) [1] working group defines physical layer (PHY) and medium access control layer (MAC) standards specifications for low data rate wireless connections operating in the personal operating space (POS) of 10 m. The LR-WPAN supports raw data rates with a maximum of 250 Kbps. In this paper we first investigate the performance and feasibility of IEEE 802.15.4 LR-WPAN for low bit-rate audio video (AV) streaming applications. We focus on important AV streaming aspects such as packet loss and latency in the performance evaluation to find a suitable operating rate range. We then propose a link quality indication (LQI) based cross-layer method for adaptive AV streaming over LR-WPANs. We show the performance of our proposed adaptive streaming approach and compare it to the non-adaptive streaming approach using simulations.

Abstract: Networks with a very large number of nodes are known to suffer from scalability problems, influencing throughput, delay, and other quality-of-service parameters. Mainly applicable to wireless sensor networks, this paper extends prior work and aims to give some fundamental indications on a scalable and optimum (or near-optimum) structuring approach for large-scale wireless networks. In: European wireless 2007, Paris, April 2007 (conference CD-ROM), 2007) and aims to give some fundamental indications on a scalable and optimum (or near-optimum) structuring approach for large-scale wireless networks. Scalability and optimality will be defined with relation to various performance criteria, an example of which is the throughput per node in the network. Various laws known from different domains will be invoked to quantify the performance of a given topology; most notably, we will make use of the well-known Kumar’s law, as well as less-known Zipf’s and other scaling laws. Optimum network structures are derived and discussed for a plethora of different scenarios, facilitating knowledgeable design guidelines for these types of networks.

in Proceedings of The IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON), pp. 108-116

inproceedings

Abstract: Sensor nodes are often organized into clusters for efficiency and scalability purposes. Every sensor cluster is managed by a cluster leader during the network operation such as routing and data aggregation. Since managing a cluster consumes substantial energy, the cluster leader needs to be re-elected from time to time for load balancing. In hostile environments, it is critical to ensure the security of such leader election. This paper proposes an efficient, resilient, and fully distributed leader election protocol for sensor networks. It only uses efficient symmetric key operations and guarantees that (i) benign cluster members will elect the same leader as long as they are well-connected, and (ii) attackers cannot impact the leader election process to increase or decrease the chance of a benign member being elected as a cluster leader. In addition, the proposed method can quickly recover from message loss or malicious attacks. The evaluation results also demonstrate the efficiency and effectiveness of this approach.

Abstract: Wireless sensor networks (WSN) are attractive for information gathering in large-scale data rich environments. In order to fully exploit the data gathering and dissemination capabilities of these networks, energy-efficient and scalable solutions for data storage and information discovery are essential. Traditionally, the communication pattern in WSNs has been assumed to be many-to-one; i.e., numerous sensors gather information which is routed to a central point commonly referred to as the sink. However, many emerging applications for WSNs require dissemination of information to interested clients within the network requiring support for differing traffic patterns. Further, in-network query processing capabilities are required for autonomic information discovery. In this paper, we formulate the information discovery problem as a load-balancing problem, with the combined aim being to maximize network lifetime and minimize query processing delay resulting in quality of service (QoS) improvements. We propose novel methods for data dissemination, information discovery and data aggregation that are designed to provide significant QoS benefits. We make use of affinity propagation to group ''similar'' sensors and have developed efficient mechanisms that can resolve both ALL-type and ANY-type queries in-network with improved energy-efficiency and query resolution time. Simulation and Analytical results prove the proposed method(s) of information discovery offer significant QoS benefits for ALL-type and ANY-type queries in comparison to previous approaches.

Abstract: Self-organization is a great concept for building scalable systems consisting of a huge number of subsystems. The primary objectives are improved scalability and dynamic adaptation to changing environmental conditions. Until now, many self-organization methods have been developed for communication networks in general and ad hoc networks in particular. Nevertheless, the term self-organization is still often misunderstood or misused. This paper contributes to the networking community by providing a better understanding of self-organization mechanisms focusing especially on the applicability in ad hoc and sensor networks. The main contributions of this paper are a clarification of the term self-organization and a categorization of self-organization methods. Additionally, well-known protocols in ad hoc and sensor networks are classified and selected case studies are provided. Primarily, solutions for the medium access control and the network layer are analyzed and discussed. Finally, open research issues with practical relevance are discussed.

Abstract: Previously proposed sensor network data dissemination schemes require periodic low-rate flooding of data in order to allow recovery from failure. We consider constructing two kinds of multipaths to enable energy efficient recovery from failure of the shortest path between source and sink. Disjoint multipath has been studied in the literature. We propose a novel braided multipath scheme, which results in several partially disjoint multipath schemes. We find that braided multipaths are a viable alternative for energy-efficient recovery from isolated and patterned failures.

Proceedings of the 23rd IEEE International Performance, Computing and Communications Conference, pp. 553–558

inproceedings

Abstract: Wireless networks have a constraint on their functional lifetime. This is due to the limited energy capacity of batteries powering the wireless nodes. For extending the lifetime of such battery-operated networks, we present a scheme for dynamically selecting the transmission rate for each node in the network. The transmission rate is based on the available energy budget in each node's battery. The goal is to increase the network capability of delivering more packets. The rate selection for each node is subject to satisfying a QoS timing constraint on the packet delivery time. Through adaptively varying each node's rate, we extended the lifetime 10 times on average more transmitting at a maximum rate and delivered on average 7.5 times more data packets. When compared with a scheme that transmits data at a lower rates independent of the battery levels, our scheme delivers up to 12% more packets for the same available total energy.

Abstract: Sensing coverage and network connectivity are two of the most fundamental problems in wireless sensor networks. Finding an optimal node deployment strategy that would minimize cost, reduce computation and communication overhead, be resilient to node failures, and provide a high degree of coverage with network connectivity is extremely challenging. Coverage and connectivity together can be treated as a measure of quality of service in a sensor network; it tells us how well each point in the region is covered and how accurate is the information gathered by the nodes. Therefore, maximizing coverage as well as maintaining network connectivity using the resource constrained nodes is a non-trivial problem. In this survey article, we present and compare several state-of-the-art algorithms and techniques that aim to address this coverageâ€“connectivity issue.

Abstract: Recently, indoor positioning systems (IPSs) have been designed to provide location information of persons and devices. The position information enables location-based protocols for user applications. Personal networks (PNs) are designed to meet the users' needs and interconnect users' devices equipped with different communications technologies in various places to form one network. Location-aware services need to be developed in PNs to offer flexible and adaptive personal services and improve the quality of lives. This paper gives a comprehensive survey of numerous IPSs, which include both commercial products and research-oriented solutions. Evaluation criteria are proposed for assessing these systems, namely security and privacy, cost, performance, robustness, complexity, user preferences, commercial availability, and limitations.We compare the existing IPSs and outline the trade-offs among these systems from the viewpoint of a user in a PN.

Abstract: This paper reports on the project plan to develop a new major version of the popular ns-2 networking simulator. The authors have organized an NSF -funded, four-year community infrastructure project to develop the next version of ns . The project will also be oriented towards community development and open source software practices to encourage participation from the broader research and educational community. The purpose of this paper is to expand on the goals and initial design concepts for this new software development effort.

Abstract: Technological progress in integrated, low-power, CMOS communication devices and sensors makes a rich design space of networked sensors viable. They can be deeply embedded in the physical world and spread throughout our environment like smart dust. The missing elements are an overall system architecture and a methodology for systematic advance. To this end, we identify key requirements, develop a small device that is representative of the class, design a tiny event-driven operating system, and show that it provides support for efficient modularity and concurrency-intensive operation. Our operating system fits in 178 bytes of memory, propagates events in the time it takes to copy 1.25 bytes of memory, context switches in the time it takes to copy 6 bytes of memory and supports two level scheduling. The analysis lays a groundwork for future architectural advances.

Electronic Notes in Theoretical Computer ScienceVol. 150(1)Proceedings of the First International Workshop on Methods and Tools for Coordinating Concurrent, Distributed and Mobile Systems (MTCoord 2005), pp. 81-101

Abstract: Mobile Ad hoc NETworks (MANETs) are dynamic networks populated by mobile stations. Stations in MANETs are usually laptops, PDAs or mobile phones. These devices feature Bluetooth and/or IEEE 802.11 (WiFi) network interfaces and communicate in a decentralized manner. Mobility is a key feature of MANETs. Because of their high cost and their lack of flexibility of such networks, experimentation is mostly achievable through simulation. Numerous tools exist for MANETs simulation, including ns-2 and GloMoSim which are the two most popular ones. This paper provides a State of the Art of MANETs simulators and associated simulation techniques. First it gives an overview of the domain. Then it provides a map of the main characteristics that MANETs simulation tools should feature and the current support of these. Finally, a description for each simulator is provided, including an explanation of what make them appealing solutions.

Abstract: Wireless local area networks (W-LANs) have become increasingly popular due to the recent availability of affordable devices that are capable of communicating at high data rates. These high rates are possible, in part, through new modulation schemes that are optimized for the channel conditions bringing about a dramatic increase in bandwidth efficiency. Since the choice of which modulation scheme to use depends on the current state of the transmission channel, newer wireless devices often support multiple modulation schemes, and hence multiple datarates, with mechanisms to switch between them Users are given the option to either select an operational datarate manually or to let the device automatically choose the appropriate modulation scheme (data rate) to match the prevailing conditions. Automatic rate selection protocols have been studied for cellular networks but there have been relatively few proposals for W-LANs. In this paper we present a rate adaptive MAC protocol called the Receiver-Based AutoRate (RBAR) protocol. The novelty of RBAR is that its rate adaptation mechanism is in the receiver instead of in the sender. This is in contrast to existing schemes in devices like the WaveLAN II [15]. We show that RBAR is better because it results in a more efficient channel quality estimation which is then reflected in a higher overall throughput Our protocol is based on the RTS/CTS mechanism and consequently it can be incorporated into many medium access control protocols including the widely popular IEEE 802.11 protocol. Simulation results of an implementation of RBAR inside IEEE 802.11 show that RBAR performs consistently well.

Abstract: This paper studies wireless sensor networks that operate in low duty cycles, measured by the percentage of time a sensor is on or active. The dynamic change in topology as a result of such duty-cycling has potentially disruptive effect on the performance of the network. We limit our attention to a class of surveillance and monitoring applications and random duty-cycling schemes, and analyze certain coverage property. Specifically, we consider coverage intensity defined as the probability distribution of durations within which a target or an event is uncovered/unmonitored. We derive this distribution using a semi-Markov model, constructed using the superposition of alternating renewal processes. We also present the asymptotic (as the number of sensors approaches infinity) distribution of the target uncovered duration when at least one sensor is required to cover the target, and provide an asymptotic lower bound when multiple sensors are required to cover the target. The analysis using the semi-Markov model serves as a tool with which we can find suitable random duty-cycling schemes satisfying a given performance requirement. Our numerical observations show that the stochastic variation of duty-cycling durations affects performance only when the number of sensors is small, whereas the stochastic mean of duty-cycling durations impacts performance in all cases studied. We also show that there is a close relationship between coverage intensity and the measure of path availability, defined as the probability distribution of durations within which a path (of a fixed number of nodes) remains available. Thus the results presented here are readily applicable to the study of path availability in a low duty-cycled sensor network.

Abstract: Advances in processor, memory and radio technology will enable small and cheap nodes capable of sensing, communication and computation. Networks of such nodes can coordinate to perform distributed sensing of environmental phenomena. In this paper, we explore the directed diffusion paradigm for such coordination. Directed diffusion is datacentric in that all communication is for named data. All nodes in a directed diffusion-based network are applicationaware. This enables diffusion to achieve energy savings by selecting empirically good paths and by caching and processing data in-network. We explore and evaluate the use of directed diffusion for a simple remote-surveillance sensor network.

Abstract: Advances in processor, memory, and radio technology will enable small and cheap nodes capable of sensing, communication, and computation. Networks of such nodes can coordinate to perform distributed sensing of environmental phenomena. In this paper, we explore the directed-diffusion paradigm for such coordination. Directed diffusion is data-centric in that all communication is for named data. All nodes in a directed-diffusion-based network are application aware. This enables diffusion to achieve energy savings by selecting empirically good paths and by caching and processing data in-network (e.g., data aggregation). We explore and evaluate the use of directed diffusion for a simple remote-surveillance sensor network analytically and experimentally. Our evaluation indicates that directed diffusion can achieve significant energy savings and can outperform idealized traditional schemes (e.g., omniscient multicast) under the investigated scenarios.

Abstract: Wireless network research in the last years is often based on simulation. Ns-2 is a widely used wireless network simulation tool for this purpose. However, there are no published results about the accuracy of the ns-2 wireless model in the literature so far. In this paper we present the validation of one wireless network model built with ns-2 done by comparing the network characteristics of a simulated, an emulated, and a real wireless network. In order to show only the relevant differences, we have calibrated the radio propagation model of ns-2 to the real network and have used the same routing protocol implementation and the same application data traffic in all the compared networks. The results show that the packet delivery ratios, the connectivity graphs, and the packet latencies are represented in the model with an average error of 0.3%, 10%, and 57% respectively. Based on these results we conclude that the packet delivery ratios, and network topologies are accurately represented in ns-2, once the simulation parameters are properly adjusted. The accuracy of the packet latencies is lower and therefore statements about latencies in the real network based on the simulation results have a lower validity. Based on these results we provide recommendations for future development of the ns-2.

Abstract: A software radio is defined as a set of digital signal processing (DSP) primitives, a metalevel system for combining the primitives into communication system functions (transmitter, channel model, receiver, etc.), and a set of target processors on which the software radio is hosted for real-time communications. The performance of enabling hardware technologies is related to software radio requirements, portending a decade of shift from hardware radios toward software intensive approaches. Computational models and architecture are discussed, stressing the need for topological consistency of radio functions and host architectures. A layered topology-oriented design approach encapsulated in a canonical open architecture software radio model is presented. The model provides a unified mathematical framework for quantitative analysis of algorithm structures, host architectures, and system performance for CAD.

Abstract: Under a multirate network scenario, the IEEE 802.11 DCF MAC fails to provide airtime fairness for all competing stations since the protocol is designed for ensuring max-min throughput fairness. As such, the maximum achievable throughput by any station gets bounded by the slowest transmitting peer. In this paper, we present an analytical model to study the delay and throughput characteristics of such networks so that the rate anomaly problem of IEEE DCF multirate networks could be mitigated. We call our proposal time fair CSMA (TFCSMA) which utilizes an interesting baseline property for estimating a target throughput for each competing station so that its minimum contention window could be adjusted in a distributed manner. As opposed to the previous work in this area, TFCSMA is ideally suited for practical scenarios where stations frequently adapt their data rates to changing channel conditions. In addition, TFCSMA also accounts for packet errors due to the time varying properties of the wireless channel. We thoroughly compare the performance of our proposed protocol with IEEE 802.11 and other existing protocols under different network scenarios and traffic conditions. Our comprehensive simulations validate the efficacy of our method toward providing high throughput and time fair channel allocation.

Abstract: We present a simulation framework to investigate the energy efficiency of different routing protocols used in resource constrained wireless sensor networks. Our simulator is modular and provides a flexible tool to build diverse protocols by combining existing building blocks at different layers and to analyse how several factors such as routing strategies, MAC protocols, link and node failures, energy on path, network topology changes, in-network processing, scheduling at MAC layer and other adjustable configuration parameters influence the energy efficiency of these protocols.\ The simulator uses and extends the open source OMNeT++ and it provides a framework to rapidly develop, to experiment with and to evaluate efficiently routing protocols; the quantitative effort to design new routing protocols and to integrate them into a complete protocol stack is considerably reduced. We provide a flexible simulation framework that supports rapid prototyping, experiments with (through simulation) and evaluation tools.

Sensor Network Protocols and Applications, 2003. Proceedings of the First IEEE. 2003 IEEE International Workshop onProceedings of the First IEEE International Workshop on Sensor Network Protocols and Applications, pp. 113-127

Abstract: We consider routing security in wireless sensor networks. Many sensor network routing protocols have been proposed, but none of them have been designed with security as a goal. We propose security goals for routing in sensor networks, show how attacks against ad-hoc and peer-to-peer networks can be adapted into powerful attacks against sensor networks, introduce two classes of novel attacks against sensor networks sinkholes and HELLO floods, and analyze the security of all the major sensor network routing protocols. We describe crippling attacks against all of them and suggest countermeasures and design considerations. This is the first such analysis of secure routing in sensor networks.

Abstract: In this paper we present a data dissemination protocol for efficiently distributing data through a sensor network in the face of node and link failures. Our work is motivated by the SPIN protocol which uses metadata negotiation to minimize data transmissions. We propose a protocol called Shortest Path Minded SPIN (SPMS) in which every node has a zone defined by its maximum transmission radius. A node which is a data source advertises the availability of data to all the nodes in its zone using a metadata descriptor. Any interested node requests the data and gets sent the data using multi-hop communication via the shortest path. The failure of any node in the path is detected and recovered using backup routes. We build simulation models to compare SPMS against SPIN. Different scenarios including mobility and node failures are simulated. The simulation results show that SPMS reduces the delay over 10 times and consumes 30 % less energy in the static failure free scenario. Even with the addition of mobility, SPMS outperforms SPIN by energy gains between 5 % and 21%. An analytical model is also constructed to compare the two protocols under a simplified topology.

Abstract: ZigBee uses the network security and application profile layers of the IEEE 802.15.4 and ZigBee Alliance standards for reliable, low-powered, wireless data communications. However, the ZigBee has problems of being less secure, and has a difficulty in distributing shared symmetric keys between each pair of nodes. In addition, the ZigBee protocol is inadequate for large sensor networks, which may consist of several very large scale clusters. In this paper, we first construct a secure ZigBee scheme for realistic scenarios consisting of a large network with several clusters containing coordinators and numerous devices. We present a new key management protocol for ZigBee networks, which can be used among participants of different clusters and analyze its performance.

International Journal of Electronics and CommunicationsVol. 61(2), pp. 69-81

article

Abstract: In sensor networks, data packets transmitted by different devices in home networking and industrial applications maintain different levels of importance. In this paper, we propose two mechanisms for IEEE 802.15.4 sensor networks to provide multi-level differentiated services which are required by each and every device. Mathematical model based on the discrete-time Markov chain is presented and is analyzed to measure the performance of the proposed mechanisms. Numerical results show the effects of the variation of contention window size and backoff exponent for service differentiation on 802.15.4 sensor networks. From the results, we derive that contention window size is more affective than backoff exponent on the saturation throughput while backoff exponent is more affective than contention window size on the average delay of every device. Simulation results are given to verify the accuracy of the numerical model.

Abstract: An implementation of an IEEE802.15.4 transceiver using software defined radio technology on a standard PC has been developed. The setup is based on the USRP, a commercially available software-defined radio hardware and on the GnuRadio software framework. The software runs on the PC to which the USRP is connected via USB2.0. The setup is ideally suited for education, monitoring, and for a deep understanding of the IEEE802.15.4 physical layer, for example for engineering students. The implemented RX software includes synchronisation, gain adjustment, a differential phase decoder, a precise symbol correlator and a data frame interface for upper software layers. The system may run on two channels synchronously. The software implementation is described with focus on the frame detection and synchronisation, the differential IQ demodulator and the correlator. It operates with an acquisition rate of 4 MSamples, each sample consisting of two IQ values.

Abstract: Conventionally, queueing analysis is performed assuming the server has a fixed service rate independent of time. If a wireless channel is the server, the service rate becomes a time-varying function due to propagation impairments. A model to quantify the performance of a queue with respect to such an impaired wireless channel is developed. Comparisons against simulation results show the model is accurate.

Abstract: Requirements for Wireless Sensor networks will increase in the future. Requirements are demanding, especially in industrial real time networks which require high reliability and performance. Network simulation tools are often needed in the network design phase before actual implementation. In this paper, we selected 5 common wireless sensor networks simulation tools and estimated their suitability for high-performance network planning and verification. According to the study, some tools managed the requirements for demanding simulation but needed some extension.

Abstract: We introduce a smart antenna (SA) module to be used in OMNeT++ for wireless sensor networks (WSN). This module is a collection of tools in OMNeT++ for adding smart antenna capability to a central node in WSNs. It is based on sectoral sweeper (SS) scheme which was shown to provide efficient task management and easy localization scheme. The number of sensing nodes, energy consumption of nodes, and data traffic carried in the network are reduced with the SS. OMNeT++ is an open source object-oriented modular discrete event network simulator consisting of hierarchically nested modules. With the SA module, desired task region can be specified by a task beam with changing beam width and beam direction parameters in the OMNeT++ configuration file. In addition, each node in the network model that uses SA module has capability of Mobility framework which is intended to support wireless and mobile simulations within OMNeT++. The simulation results provide performance evaluation using the developed module in OMNeT++ for WSNs.

Abstract: This paper addresses the performance limits of the IEEE 802.15.4 standard 2.4 GHz PHY for wireless personal area and sensor networks. As designers start considering the addition of power amplifiers to improve link margin, other methods that do not increase power significantly are of high value. Minimizing power consumption is the key goal of 802.15.4 systems, and improvements in sensitivity can be traded for power savings. The limits from communication theory are compared to the performance of common system topologies, and methods for improving system performance without significant cost are discussed and verified through simulation. Approximately 6.6 dB of sensitivity is shown to be commonly sacrificed, and 5.8 dB is recoverable without large increases in design complexity.

Abstract: Emerging data streaming applications in Wireless Sensor Networks require reliable and energy-efficient Transport Protocols. Our recent Wireless Sensor Network deployment in the Burdekin delta, Australia, for water monitoring [T. Le Dinh, W. Hu, P. Sikka, P. Corke, L. Overs, S. Brosnan, Design and deployment of a remote robust sensor network: experiences from an outdoor water quality monitoring network, in: Second IEEE Workshop on Practical Issues in Building Sensor Network Applications (SenseApp 2007), Dublin, Ireland, 2007] is one such example. This application involves streaming sensed data such as pressure, water flow rate, and salinity periodically from many scattered sensors to the sink node which in turn relays them via an IP network to a remote site for archiving, processing, and presentation. While latency is not a primary concern in this class of application (the sampling rate is usually in terms of minutes or hours), energy-efficiency is. Continuous long-term operation and reliable delivery of the sensed data to the sink are also desirable.

This paper proposes ERTP, an Energy-efficient and Reliable Transport Protocol for Wireless Sensor Networks. ERTP is designed for data streaming applications, in which sensor readings are transmitted from one or more sensor sources to a base station (or sink). ERTP uses a statistical reliability metric which ensures the number of data packets delivered to the sink exceeds the defined threshold. Our extensive discrete event simulations and experimental evaluations show that ERTP is significantly more energy-efficient than current approaches and can reduce energy consumption by more than 45% when compared to current approaches. Consequently, sensor nodes are more energy-efficient and the lifespan of the unattended WSN is increased.

Abstract: IEEE 802.15.4 is an emerging standard specifically designed for low-rate wireless personal area networks (LR-WPAN) with a focus on enabling the wireless sensor networks. It attempts to provide a low data rate, low power, and low cost wireless networking on the device-level communication. In this paper, we have established a realistic environment for the preliminary performance evaluation of the IEEE 802.15.4 wireless networks. Several sets of practical experiments are conducted to study its various features, including the effects of 1) the direct and indirect data transmissions, 2) CSMA-CA mechanism, 3) data pay load size, and 4) beacon-enabled mode. The data throughput, delivery ratio, and received signal strength indication (RSSI) are investigated as the performance metrics. The results show that IEEE 802.15.4 has better performance in non-beacon mode. Some issues that could degrade the network performance are also discussed in this paper.

Abstract: This paper presents a distributed fault detection algorithm for wireless sensor networks. Faulty sensor nodes are identified based on comparisons between neighboring nodes and dissemination of the decision made at each node. Time redundancy is used to tolerate transient faults in sensing and communication. To eliminate delay involved in time redundancy scheme a sliding window is employed with some storage for previous comparison results. Simulation results show that sensor nodes with permanent faults are identified with high accuracy for a wide range of fault rates, while most of the transient faults are tolerated with negligible performance degradation.

Abstract: In order to evaluate the behavior and performance of protocols for wireless networks, simulations are a good compromise between cost and complexity, on the one hand, and accuracy of the results, on the other hand. Since there are many simulators for wireless networks, it is often difficult to decide which simulator to choose. To help shed light on this issue, we present a case study in which four popular wireless network simulators were used to evaluate a well-known topology control protocol (SPAN). Within the case study, we describe outstanding and desirable but missing features of the simulators, outlining their strengths and weaknesses. Further, we compare the amount of effort needed for installation, familiarization, implementation (needed lines of code and lines for configuration) and visualization. As opposed to other simulator comparisons, we do not focus on the correlation of the individual simulation results, but try to compare the simulators from feature and usability point of view. This paper can help other researchers to quickly identify which simulator is most suitable for their needs.

Abstract: A novel call admission control (CAC) scheme for an adaptive heterogeneous multimedia mobile network with multiple classes of calls is investigated here. Different classes of calls may have different bandwidth requirement, different request call holding time and different cell residence time. At any time, each cell of the network has the capability to provide service to at least a given number of calls for each class of calls. Upon the arrival (or completion or hand off) of a call, a bandwidth degrade (or upgrade) algorithm is applied. An arriving call to a cell, finding insufficient bandwidth available in this cell, may either be disconnected from the network or push another call out of the cell toward a neighboring cell with enough bandwidth. We first prove that the stationary distribution of the number of calls in the network has a product form and then show how to apply this result in deriving explicit expressions of handoff rates for each class of calls, in obtaining the disconnecting probabilities for each class of new and handoff calls, and in finding the grade of service of this mobile network.

Abstract: An analytic model of cellular mobile communications networks with instantaneous movement is investigated in this paper. This cellular mobile network is showed to be equivalent to a queueing network and furthermore the equilibrium distribution of this cellular mobile network is proved to have a product form. The explicit expressions for handoff rates of calls from one cell to another, the blocking probability of new calls and handoff calls are then obtained. Actual call connection time (ACCT) of a call in this cellular mobile network is characterized in detail, which is the total time a mobile user engages in communications over the network during a call connection and can be used to design appropriate charging schemes. The average ACCT for both complete call and incomplete call, as well as the probability for a call to be incomplete or complete, are derived. Our numerical results show how the above measures depend on the new call arrival process for some specific reserved channels numbers in each cell. The results presented in this paper are expected to be useful for the cost analysis for updating location and paging in cellular mobile network.

Abstract: In this paper, we propose the expected schedulability to characterize the schedulability for the stochastic tasks on a single real-time computer processor. Our results show that the stochastic model has more flexibility to characterize the real-time tasks than the deterministic model. The expected schedulability is related to the real-time t at tasks arrival and may show that a sub-set of task would be scheduled at any given real-time interval. The numerical analysis based on our theoretic results is consistent with the simulation analysis. Both numerical and simulation results show that the tasks would be scheduled for real-time tasks in realtime systems if the traffic load is less than a specific value which is more than 69%, which was provided in some deterministic situations. This observation implies that the expected schedulability based on the stochastic model would provide a bigger threshold for the real-time tasks to be scheduled.

Abstract: Real-time wireless sensor networks are becoming more and more important by the requirement of message delivery timeliness in emerging new applications. Supporting real-time QoS in sensor networks faces severe challenges due to the wireless nature, limited resource, low node reliability, distributed architecture and dynamic network topology. There are tradeoffs between different application requirements including energy efficiency and delay performance. This paper studies the state of the art of current real-time solutions including MAC protocols, routing protocols, data processing strategies and cross-layer designs. Some research challenges and future design favors are also identied and discussed.

Abstract: Low power wireless sensors are limited by current radio technologies to short communication range and low throughput. We envision that future radios with advanced software programmable encoding and modulation will bring sensor networks unprecedented flexibility and performance. We have taken a step towards realizing this vision by designing a softwarebased, narrow-band transceiver using the GNU Radio software and the Universal Software Radio Peripheral hardware. We have verified the compatibility of our implementation with existing wireless sensor platforms. We demonstrate the flexibility of our design with sensing applications running on a sensor network communicating over hybrid radios.

Abstract: One of severe security threats in wireless sensor network is node compromise. A compromised node can easily inject false data reports on the events that do not occur. The existing approaches in which each forwarding sensor along a path probabilistically filters out injected false data may not be adequate because such protection may break down when more than a threshold number of nodes are compromised. To solve this problem, we present a sink filtering scheme in clusters of heterogeneous sensor networks. In addition to basic sensors, some powerful data gathering sensors termed as cluster heads (CHs) are added. Each aggregation report generated by a CH must carry multiple keyed message authentication codes (MACs); each MAC is generated by a basic sensor that senses the event. The sink node checks the validity of the carried MACs in an aggregation report and filters out the forged report. We analyze the resilience and overhead of the sink filtering scheme. Both analytical and simulation results show that the scheme is resilient to an increasing number of compromised nodes, with graceful performance degradation. Particularly, we adopt Poisson Approximation to investigate the performance tradeoff between resilience and overall cost, and give some suggestions on how to choose the parameters. The scheme is also scalable and efficient in communication, computation and storage.

Abstract: In an IEEE 802.11 multirate network, the aggregate system throughput is unfavorably dominated by stations with the lowest data rate. To improve the performance, it is required to provide airtime fairness for stations regardless of their data rates. Unfortunately, the IEEE 802.11 MAC protocol DCF (Distributed Coordination Function) fails to satisfy this requirement. In this paper, we propose an adaptive MAC scheme, named Time Fairness Transmission Control (TFTC), to maximize the system throughput while maintaining airtime fairness among the competing stations. Specifically, making use of the information provided to each station by the carrier sensing mechanism, TFTC dynamically adjusts the transmission probabilities for stations transmitting at each data rate. As opposed to the previous works, our proposed scheme has strong ability to lead the network to work under near optimal state without the requirement of estimating the number of active stations in the network. Performance evaluation results show that the scheme is effective in achieving near to the theoretical maximum system throughput and providing time fair channel allocation among stations with different data rates.

Abstract: A critical issue for data gathering in wireless sensor networks is the formation of energy holes near the sinks. Sensors near the sinks have to participate in relaying data on behalf of other sensors and thus will deplete their energy very quickly, resulting in network partitioning and limitation of the network lifetime. The solution that we propose in this paper is to use mobile sinks that change their location when the nearby sensors’ energy becomes low. In this way the sensors located near sinks change over time. In deciding a new location, a sink searches for zones with richer sensor energy.

First, we study the improvement in network lifetime when sinks move on a predetermined path, along the perimeter of a hexagonal tiling. Two cases are considered for data gathering when sinks stop in the hexagon’s corners and when the sinks stop on multiple locations on the hexagon perimeter. This study shows an improvement of up to 4.86 times in network lifetime. Second, we design a distributed and localized algorithm used by the sinks to decide their next movement location such that the virtual backbone formed by the sinks remains interconnected at all times. Two extensions of the distributed algorithm, coverage requirement and limitation of the time-delivery requirement, are also addressed. Simulation results are presented to verify our approaches.

IEEE International Symposium on Advanced Networks and Telecommunication Systems (ANTS)

inproceedings

Abstract: A popular physical layer used in wireless sensor networks is the IEEE 802.15.4 standard, which provides for a single coding scheme with constant data rate regardless of channel properties and noise conditions. This paper proposes and simulates a simple steganography method to embed additional information in 802.15.4 data packets when link quality permits, with a modest increase in signal to noise ratio (SNR) required for the same error performance of the underlying 802.15.4 communication. By expanding the code set to include a cluster of 31 ancillary codes for each original 802.15.4 code word, 5 bits can be steganographically overlaid on each 4 bit legacy symbol, allowing this additional data to be transmitted without the knowledge of legacy 802.15.4 receivers over links of greater than 1.95 dB SNR. Increasing the information content by 3.5 dB in this manner can lower the overall energy per bit to noise ratio by 0.1 dB.

Abstract: Currently, few real sensor web applications are being explored and some of them are yet to come. Meanwhile, developing and deploying prototypes in order to analyze the sensor web performance supposes a great effort. Consequently, simulation is fundamental to study sensor webs, and is being the common way to test new applications and protocols in this evolving research field. This fact has brought a recent growing number of simulation tools available to model sensor webs. In this paper, we provide background on a number of different sensor webs simulation tools and we discuss the advantages and the drawbacks of each. We also propose an evaluation methodology in order to assess the capabilities of each simulation tool. The results of the evaluation process are analyzed and the open research issues are pointed out providing for an opportunity of improvement of future sensor web simulators.

Abstract: Recent technological advances in sensors, low-power integrated circuits, and wireless communications have enabled the design of low-cost, miniature, lightweight, and intelligent physiological sensor nodes. These nodes, capable of sensing, processing, and communicating one or more vital signs, can be seamlessly integrated into wireless personal or body networks (WPANs or WBANs) for health monitoring. These networks promise to revolutionize health care by allowing inexpensive, non-invasive, continuous, ambulatory health monitoring with almost realtime updates of medical records via the Internet. Though a number of ongoing research efforts are focusing on various technical, economic, and social issues, many technical hurdles still need to be resolved in order to have flexible, reliable, secure, and power-efficient WBANs suitable for medical applications. This paper discusses implementation issues and describes the authors’ prototype sensor network for health monitoring that utilizes off-the-shelf 802.15.4 compliant network nodes and custom-built motion and heart activity sensors. The paper presents system architecture and hardware and software organization, as well as the authors ’ solutions for time synchronization, power management, and on-chip signal processing.

Abstract: Continuous mobility scenarios are those in which applications continue to use the radio interface while on the move. With the emergence of Voice-over-WiFi phones, WiFi-enabled music players, and many other such gadgets, continuous mobility is becoming a prevalent mode of operation for WiFi standards. We contend that the existing packetization structures employed in WiFi devices, is not the most suitable for these emerging class of continuous mobility applications. Therefore, in this paper, we suggest a new software-level, standards-compliant extension to the WiFi packetization techniques that provides greater agility and improved performance. In particular, we propose the notion of a multi-rate wireless packet, in which different segments of the same Protocol Data Unit (PDU) are modulated at different physical transmission rates. This is a departure from conventional modulation mechanisms in which the entire PDU is modulated using a single rate. In this paper, we (i) discuss some uses of such a packetization structure for continuous mobility applications, (ii) describe a practical approach to implementing multi-rate wireless packetization in the 802.11 context as a software-only modification that directly leverages current PHY and MAC layer implementations, and (iii) demonstrate the benefits of such an approach with some simple evaluation. We conclude by discussing some of the next steps needed to realize the full potential of this notion.

Abstract: The Gilbert-Elliott channel, a varying binary symmetric channel, with crossover probabilities determined by a binary-state Markov process, is treated. In general, such a channel has a memory that depends on the transition probabilities between the states. A method of calculating the capacity of this channel is introduced and applied to several examples, and the question of coding is addressed. In the conventional usage of varying channels, a code suitable for memoryless channels is used in conjunction with an interleaver, with the decoder considering the deinterleaved symbol stream as the output of a derived memoryless channel. The transmission rate is limited by the capacity of this memoryless channel, which is often considerably less than the capacity of the original channel. A decision-feedback decoding algorithm that completely recovers this capacity loss is introduced. It is shown that the performance of a system incorporating such an algorithm is determined by an equivalent genie-aided channel, the capacity of which equals that of the original channel. The calculated random coding exponent of the genie-aided channel indicates a considerable increase in the cutoff rate over that of the conventionally derived memoryless channel.

Abstract: Research on wireless sensor networks (WSNs) has received tremendous attention in the past few years due to their potential applications and advances in the VLSI design. In WSNs with tiny sensors, mobility of a sink may provide an energy efficient way for data dissemination. Having a mobile sink in WSN, however, creates new challenges to routing and sensor distribution modeling in the network. In this paper, based on clustering and routing optimization algorithms, we propose a new scheme called K-means and TSP-based mobility (KAT mobility). After clustering the sensor nodes, the proposed method navigates the mobile sink to traverse through the cluster centers according to the trajectory of an optimized route. The mobile sink then collects the data from sensors at the visited clusters. Simulation results have demonstrated that the proposed scheme can provide not only better energy efficiency as compared to those obtained by conventional methods which assume random waypoint for the mobile sink, but also fault-resilience in case of malfunctions of some sensors due to attacks.

Abstract: he new IEEE 802.15.4 standard enables deployment of low-rate low-power personal area networks. It provides a mechanism for adaptation of the protocols duty cycle during runtime. In this paper we propose BOAA, a new algorithm for beacon order adaptation in IEEE 802.15.4 star-topology networks. By observing the communication frequency, the coordinator in such a network determines the required duty cycle and adapts the beacon interval accordingly. Investigations reveal that the algorithm enables power saving with a trade-off according to message delay.

Abstract: This paper presents a study on three simulation tools for Wireless Sensor Nertworks (WSNs): Network Simulator 2 (ns-2), Java Simulator (J-Sim) and Sensor Network Emulator and Simulator (SENSE). We present the concept of WSNs, each simulator in terms of its features, a view on current applications of WSNs on medicine and a comparative study on the simulators studied. We conclude that SENSE presents the better approach for WSNs.

Abstract: A Wireless Sensor Network is composed of up to thousands of smart sensing nodes with processing unit and memory, sensing unit and wireless communication capabilities. Wireless Sensor Networks application spans from the military applications into almost every field we can think of. Several simulation tools are readily available and, among them, the J-Sim is a java-based simulator with growing interest by research and network developers alike. In this paper, we propose to enhance J-Sim functionality with a Guided User Interface for Wireless Sensor Networks that dramatically increases the user-friendliness of the simulator. Also, we provide a free download web page for everyone to benefit.

Abstract: In a wireless sensor network, multiple nodes would send sensor readings to a base station for further processing. It is known that such a many-to-one communication is highly vulnerable to a sinkhole attack, where an intruder attracts surrounding nodes with unfaithful routing information, and then performs selective forwarding or alters the data passing through it. A sinkhole attack forms a serious threat to sensor networks, particularly considering that the sensor nodes are often deployed in open areas and of weak computation and battery power. In this paper, we present a novel algorithm for detecting the intruder in a sinkhole attack. The algorithm first finds a list of suspected nodes through checking data consistency, and then effectively identifies the intruder in the list through analyzing the network flow information. The algorithm is also robust to deal with multiple malicious nodes that cooperatively hide the real intruder. We have evaluated the performance of the proposed algorithm through both numerical analysis and simulations, which confirmed the effectiveness and accuracy of the algorithm. Our results also suggest that its communication and computation overheads are reasonably low for wireless sensor networks.

Abstract: There is a critical need for more cost efficient solutions for supervision/monitoring patients during and after surgery, as well as when the patient is at home. Advanced sensors combined with wireless communication will give reduced costs, improved monitoring, and better life quality for the patient. This project developed, implemented and tested a first version of a biomedical sensor network for the future wireless hospital and home care. The sensor network comprised four different sensors, and was tested in a hospital environment.

Abstract: This paper describes the development of the next generation of an extremely compact, wireless impedance sensor node for use in structural health monitoring (SHM) and piezoelectric active-sensor self-diagnostics. The sensor node uses a recently developed, low-cost integrated circuit that can measure and record the electrical impedance of a piezoelectric transducer. The sensor node also integrates several components, including a microcontroller for local computing, telemetry for wirelessly transmitting data, multiplexers for managing up to seven piezoelectric transducers per node, energy harvesting and storage mediums, and a wireless triggering circuit into one package to truly realize a comprehensive, self-contained wireless active-sensor node for various SHM applications. It is estimated that the developed sensor node requires less than 60 mW of total power for measurement, computation, and transmission. In addition, the sensor node is equipped with active-sensor self-diagnostic capabilities that can monitor the condition of piezoelectric transducers used in SHM applications. The performance of this miniaturized device is compared to our previous results and its broader capabilities are demonstrated.

Abstract: Wireless sensor networks often consists of a large number of low-cost sensor nodes that have strictly limited sensing, computation, and communication capabilities. Due to resource restricted sensor nodes, it is important to minimize the amount of data transmission so that the average sensor lifetime and the overall bandwidth utilization are improved. Data aggregation is the process of summarizing and combining sensor data in order to reduce the amount of data transmission in the network. As wireless sensor networks are usually deployed in remote and hostile environments to transmit sensitive information, sensor nodes are prone to node compromise attacks and security issues such as data confidentiality and integrity are extremely important. Hence, wireless sensor network protocols, e.g., data aggregation protocol, must be designed with security in mind. This paper investigates the relationship between security and data aggregation process in wireless sensor networks. A taxonomy of secure data aggregation protocols is given by surveying the current "state-of-the-art"work in this area. In addition, based on the existing research, the open research areas and future research directions in secure data aggregation concept are provided.

Abstract: Emerging high-rate applications (imaging, structural monitoring, acoustic localization) will need to transport large volumes of data concurrently from several sensors. These applications are also loss-intolerant. A key requirement for such applications, then, is a protocol that reliably transport sensor data from many sources to one or more sinks without incurring congestion collapse. In this paper, we discuss RCRT, a rate-controlled reliable transport protocol suitable for constrained sensor nodes. RCRT uses end-to-end explicit loss recovery, but places all the congestion detection and rate adaptation functionality in the sinks. This has two important advantages: efficiency and flexibility. Because sinks make rate allocation decisions, they are able to achieve greater efficiency since they have a more comprehensive view of network behavior. For the same reason, it is possible to alter the rate allocation decisions (for example, from one that ensures that all nodes get the same rate, to one that ensures that nodes get rates in proportion to their demands), without modifying sensor code at all. We evaluate RCRT extensively on a 40-node wireless sensor network testbed and show that RCRT achieves more than twice the rate achieved by a recently proposed interference-aware distributed rate-control protocol, IFRC [23].

Abstract: Power saving is a very critical issue in energy-constrained wireless sensor networks. Many schemes can be found in the literature, which have significant contributions in energy conservation. However, these schemes do not concentrate on reducing the end-to-end packet delay while at the same time retaining the energy-saving capability. Since a long delay can be harmful for either large or small wireless sensor networks, this paper proposes a TDMA-based scheduling scheme that balances energy-saving and end-to-end delay. This balance is achieved by an appropriate scheduling of the wakeup intervals, to allow data packets to be delayed by only one sleep interval for the end-to-end transmission from the sensors to the gateway. The proposed scheme achieves the reduction of the end-to-end delay caused by the sleep mode operation while at the same time it maximizes the energy savings.

Abstract: Economic and reliable online health monitoring strategies are very essential for safe operation of civil, mechanical and aerospace structures. This study presents online structural health monitoring (SHM) techniques using wireless impedance sensor nodes equipped with both functions of structural damage identification and sensor self-diagnosis. The wireless impedance sensor node incorporating a miniaturized impedance measuring chip, a microcontroller and radio-frequency (RF) telemetry is equipped with the capabilities for temperature sensing, multiplexing of several sensors, and local data analysis. The feasibility of the sensor node for structural damage identification is firstly investigated through a series of experimental studies inspecting loosened bolt damage and cut damage cases. Additionally, a temperature effects-free sensor self-diagnosis algorithm is embedded into the sensor node and its feasibility is examined from the experiments monitoring the integrity of each piezoelectric sensor on a wireless sensor network.

Abstract: This article describes architectural and algorithmic approaches that designers can use to enhance the energy awareness of wireless sensor networks. The article starts off with an analysis of the power consumption characteristics of typical sensor node architectures and identifies the various factors that affect system lifetime. We then present a suite of techniques that perform aggressive energy optimization while targeting all stages of sensor network design, from individual nodes to the entire network. Maximizing network lifetime requires the use of a well-structured design methodology, which enables energy-aware design and operation of all aspects of the sensor network, from the underlying hardware platform to the application software and network protocols. Adopting such a holistic approach ensures that energy awareness is incorporated not only into individual sensor nodes but also into groups of communicating nodes and the entire sensor network. By following an energy-aware design methodology based on techniques such as in this article, designers can enhance network lifetime by orders of magnitude

Abstract: Pervasive computing environments find their practical manifestations through wireless sensor networks, which sense a relationship amongst themselves and the environment. Currently the proposed keying schemes for ensuring security, in wireless sensor networks, may be classified into public and private keying schemes, or their hybrid. However, an investigation in peer work underpins the fact that neither of these works relates the key management schemes with the granularity of key generation, distribution, renewal, and revocation. In this paper, we propose a unified security framework with three key management schemes, SACK, SACK-P, and SACK-H that incorporate symmetric key cryptography, asymmetric key cryptography and the hybrid, respectively. We have evaluated the key management schemes against a broad range of metrics such as energy, resource utilization, scalability and resilience to node compromises. Our evaluation comprises both analytical investigation and experimental validation. The results show that though SACK-P is heavy on resources, it provides maximal security and offers the best resilience to node compromises. On the contrary, SACK is very efficient in terms of storage and communication. Our results substantiate a relationship between the level of security and resource utilization and form a design benchmark for security frameworks.

Abstract: Wireless Sensor Networks (WSNs) have the potential of significantly enhancing our ability to monitor and interact with our physical environment. Realizing a fault tolerant operation is critical to the success of WSNs. The main challenge is providing fault tolerance (FT) while conserving the limited resources of the network. Many schemes have been proposed in this area. Our main contribution in this paper is to propose a general framework for fault tolerance in WSNs. The proposed framework can be used to guide the design and development of FT solutions and to evaluate existing ones. We present a comparative study of the existing schemes and identify potential enhancements. A primary module of the framework is the learning and refinement module which enables a FT solution to be adaptive and self-configurable based on changes in the network conditions. We view this as vital to the resource-constrained and highly dynamic WSNs. Up to our knowledge, we are the first to propose the implementation of such module in FT solutions for WSNs.

Abstract: The IEEE wireless standard 802.15.4 gets widespread attention because of its adoption in sensor networks, home automation, and other networked systems. The goal of the project is to implement an en- and decoding block for the IEEE 802.15.4 protocol in GNU Radio, an open source solution for software defined radios. This report will give an insight into the working of GNU Radio and some of its hardware components. Additionally, it gives details about the implementation of the en- and decoding blocks. At the end, we will verify the implementation by sending and receiving messages to and from an actual IEEE 802.15.4 radio chip, the CC2420 from ChipCon, and give a small bandwidth comparison of the two solutions.

Abstract: Software Defined Radios are becoming more and more prevalent. Especially in the radio amateur community, Software Defined Radios are a big success. The wireless industry also has considerable interest in the dynamic reconfigurability and other advantages of Software Defined Radios. Our research focuses on the latency of Software Defined Radios and its impact on throughput in modern wireless protocols. Software Defined Radio systems often employ a bus system to transfer the samples from a radio frontend to the processor which introduces a non-negligible latency. Additionally, the signal processing calculations on general-purpose processors introduce additional latencies that are not found on conventional radios. This work concentrates on one particular Software Defined Radio system called GNU Radio, an open source Software Defined Radio application, and one of its hardware components, the Universal Software Radio Peripheral (USRP), and analyzes its receive and transmit latencies. We will use these measurements to characterize the performance impact on IEEE 802.15.4 implementation in GNU Radio. Additionally, we present two Software Defined Radio implementations of short-range radio standards, a FSK scheme used in the Chipcon CC1000 radio, and the physical layer of IEEE 802.15.4. We use these implementations for round trip time measurements and introduce two sample applications, a physical layer bridge between the FSK scheme and IEEE 802.15.4, and a dual channel receiver that receives two radio channels concurrently.

Abstract: Mobile devices in the IEEE 802.11 wireless local area network (WLAN) have the ability to transmit data frames at one of four transmission rates 1Mb/s, 2Mb/s, 5.5Mb/s and 11Mb/s. This is because the commercial WLAN transceivers are equipped with several modulation schemes. According to the characteristics of the modulation scheme, a higher transmission rate will result in a smaller transmission range and longer time consumption on data frame transmission. If the channel environment is relatively clear and the transmission distance is short, one should choose a higher transmission rate for data transmission to maximise channel utilisation. On the contrary, a lower transmission rate should be selected to minimise the frame loss and frame error probabilities if the bit error rate is high. Therefore, the problem of choosing a proper transmission rate to accommodate a varying environment is a new and valuable problem in the wireless LANs. To our knowledge, it is very difficult and impractical to formalise an indoor environment since the channel status is quite unstable and unpredictable. Instead, we propose an adaptive rate controller (ARC), which employs the powerful fuzzy set function, for intelligently selecting the transmission rate for frame transmissions. This fuzzy control function refers the received signal strength indicator (RSSI), the frame error rate (FER) and the medium access control (MAC) delay to make a correct decision. Simulation results demonstrate that the proposed fuzzy controller indeed enhances the network throughput and the access delay.

Abstract: Sensor networks face many problems that do not arise inother types of networks. Power constraints, limited hardware,decreased reliability, and a typically higher density andnumber of nodes than found in conventional networks are justa small portion of the problems that have to be consideredwhen developing protocols for use in sensor networks.Simulation is often used to test new protocols that are beingdeveloped, as well as to compare old protocols. However,there is always a danger when using simulation in testing: theresults are not necessarily going to be accurate orrepresentative. To help overcome this, it is important topossess knowledge of the simulation tools available, alongwith their associated strengths and weaknesses. The goal ofthis paper is to aid developers in the selection of anappropriate simulation tool.

Abstract: We present a suite of algorithms for self-organization of wireless sensor networks in which there is a scalably large number of mainly static nodes with highly constrained energy resources. The protocols further support slow mobility by a subset of the nodes, energy-efficient routing, and formation of ad hoc subnetworks for carrying out cooperative signal processing functions among a set of the nodes

Abstract: In this paper, we have developed a Low cost and low power Wireless Sensor Networks (WSNs) Node using MSP430 and Nordic nRF24L01. The architectural and circuit details are presented. This architecture fulfils the requirements of low power, compact size and self-organization with a new feature of adaptive Power Control. For Low power consumption Adaptive Power control technique is used. In this technique we can vary the transmitted power according to the distance between the nodes, which is also the different feature of this WSN. Adaptive power algorithm that uses both RF output Power and Transmission rate to be adjusted according to the distance between the Nodes which will maximize the battery life time. All the Radio modules available in the market are utilizing constant power transmission during its operation. Hence significant reduction in energy consumption is possible based on the proposed approach which prolongs the battery lifetime.

Abstract: Health monitoring of reinforced concrete bridges and other large-scale civil infrastructures has received considerable attention in recent years. However, traditional inspection methods (x-ray, C-scan, etc) are expensive and sometimes ineffective for large-scale structures. Piezoceramic transducers have emerged as new tools for the health monitoring of large-scale structures due to their advantages of active sensing, low cost, quick response, availability in different shapes, and simplicity for implementation. In this research, piezoceramic transducers are used for damage detection of a 6.1 m long reinforced concrete bridge bent-cap. Piezoceramic transducers are embedded in the concrete structure at pre-determined spatial locations prior to casting. This research can be considered as a continuation of an earlier work, where four piezoceramic transducers were embedded in planar locations near one end of the bent-cap. This research involves ten piezoceramic patches embedded at spatial locations in four different cross-sections. To induce cracks in the bent-cap, the structure is subjected to loads from four hydraulic actuators with capacities of 80 and 100 ton. In addition to the piezoceramic sensors, strain gages, LVDTs, and microscopes are used in the experiment to provide reference data. During the experiment, one embedded piezoceramic patch is used as an actuator to generate high frequency waves, and the other piezoceramic patches are used as sensors to detect the propagating waves. With the increasing number and severity of cracks, the magnitude of the sensor output decreases. Wavelet packet analysis is used to analyze the recorded sensor signals. A damage index is formed on the basis of the wavelet packet analysis. The experimental results show that the proposed methods of using piezoceramic transducers along with the damage index based on wavelet packet analysis are effective in identifying the existence and severity of cracks inside the concrete structure. The experimental results demonstrate that the proposed method has the ability to predict the failure of a concrete structure as verified by results from conventional microscopes (MSs) and LVDTs.

Abstract: This paper summarizes the authors' recent pioneering research work in piezoceramic-based smart aggregates and their innovative applications in concrete civil structures. The basic operating principle of smart aggregates is first introduced. The proposed smart aggregate is formed by embedding a waterproof piezoelectric patch with lead wires into a small concrete block. The proposed smart aggregates are multi-functional and can perform three major tasks: early-age concrete strength monitoring, impact detection and structural health monitoring. The proposed smart aggregates are embedded into the desired location before the casting of the concrete structure. The concrete strength development is monitored by observing the high frequency harmonic wave response of the smart aggregate. Impact on the concrete structure is detected by observing the open-circuit voltage of the piezoceramic patch in the smart aggregate. For structural health monitoring purposes, a smart aggregate-based active sensing system is designed for the concrete structure. Wavelet packet analysis is used as a signal-processing tool to analyze the sensor signal. A damage index based on the wavelet packet analysis is used to determine the structural health status. To better describe the time-history and location information of damage, two types of damage index matrices are proposed: a sensor-history damage index matrix and an actuator–sensor damage index matrix. To demonstrate the multi-functionality of the proposed smart aggregates, different types of concrete structures have been used as test objects, including concrete bridge bent-caps, concrete cylinders and a concrete frame. Experimental results have verified the effectiveness and the multi-functionality of the proposed smart aggregates. The multi-functional smart aggregates have the potential to be applied to the comprehensive monitoring of concrete structures from their earliest stages and throughout their lifetime.

Abstract: Earlier sensor network MAC protocols focus on energy conservation in low-duty cycle applications, while some recent applications involve real-time high-data-rate signals. This motivates us to design an innovative localized TDMA MAC protocol to achieve high throughput and low congestion in data collection sensor networks, besides energy conservation. TreeMAC divides a time cycle into frames and each frame into slots. A parent node determines the children’s frame assignment based on their relative bandwidth demand, and each node calculates its own slot assignment based on its hop-count to the sink. This innovative 2-dimensional frame-slot assignment algorithm has the following nice theory properties. First, given any node, at any time slot, there is at most one active sender in its neighborhood (including itself). Second, the packet scheduling with TreeMAC is bufferless, which therefore minimizes the probability of network congestion. Third, the data throughput to the gateway is at least 1/3 of the optimum assuming reliable links. Our experiments on a 24-node testbed show that TreeMAC protocol significantly improves network throughput, fairness, and energy efficiency compared to TinyOS’s default CSMA MAC protocol and a recent TDMA MAC protocol Funneling-MAC. Partial results of this paper were published in Song, Huang, Shirazi and Lahusen [W.-Z. Song, R. Huang, B. Shirazi, and R. Lahusen, TreeMAC: Localized TDMA MAC protocol for high-throughput and fairness in sensor networks, in: The 7th Annual IEEE International Conference on Pervasive Computing and Communications, PerCom, March 2009]. Our new contributions include analyses of the performance of TreeMAC from various aspects. We also present more implementation detail and evaluate TreeMAC from other aspects.

Abstract: Recently, security issues in wireless sensor networks become more important. Many mechanisms have been proposed for solving varying types of malicious attacks. However, few of them discussed malicious packet-modifying attacks (MPA). The MPA come from some malicious nodes that modify contents of data packets while relaying. Once MPA occur, the sink node may make wrong decisions according to the incorrect packets. In this paper, an overhearing-based detection mechanism (OBD) is presented for detecting the occurrence of MPA. Both OBD and a traditional two-path detection mechanism were successfully implemented for comparison using the NS2. The simulation measured the metrics in successful detection rate, end-to-end delay, power consumption, and detection latency. Compared to the two-path detection mechanism, the overhearing-based mechanism not only incurred less overhead but provided more accurate failure detection performance.

Abstract: Recent advances in micro-electromechanical (MEMS) technology have led to the development of small, low-cost, and low-power sensors. Wireless sensor networks (WSNs) are large-scale networks of such sensors, dedicated to observing and monitoring various aspects of the physical world. In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable. This paper surveys and evaluates existing clock synchronization protocols based on a palette of factors like precision, accuracy, cost, and complexity. The design considerations presented here can help developers either in choosing an existing synchronization protocol or in defining a new protocol that is best suited to the specific needs of a sensor-network application. Finally, the survey provides a valuable framework by which designers can compare new and existing synchronization protocols.

Abstract: In this paper we propose a system architecture for enabling mobile nodes to query a largely deployed wireless sensor network in an intelligent transportation system scenario. We identify three different types of nodes in the network: mobile sinks (i.e. the nodes moving and querying the WSN), vice-sinks (i.e. nodes able to communicate directly with mobile sinks) and ordinary sensor nodes (i.e. nodes sensing a phenomenon and communicating in a multihop fashion). We present protocols and algorithms specifically tailored to such a scenario, in particular at the MAC and network layers. Such a reference architecture well covers situations in which WSNs deployed in a parking place or along a road, provide to cars information on the conditions of the surrounding environment. We introduce and analyse a simple geographic routing protocol and two different load balancing techniques. The performance of the proposed solutions is evaluated through extensive simulations. The simple geographic routing is compared to load balancing techniques. Results support the capability of the proposed solutions to enable the introduction of novel intelligent transportation system applications.

Review: Wireless sensor networks (WSNs) have become a very active and important area of research due to their potential in civil and military applications. A lot of research works focus on energy efficient routing protocols due to the limited energy of battery-powered nodes. Currently, the increasing interest in multimedia applications has made the QoS (quality of service) supporting an unavoidable task. In this paper, we perform the analysis of QoS supporting and optimal energy allocation issues by presenting a cluster based WSN. A QoS supporting scheme is developed for dynamic traffic conditions by controlling data generating rates at individual clusters. In addition, an explicit solution on the energy distribution at different clusters in the WSN is investigated based on an optimal energy allocation criterion. The localized QoS controlling scheme is useful in WSNs due to flexibility and scalability, and the obtained network energy distribution formula is particularly convenient for node deployment design in WSNs and three specific situations are discussed as applications.

Abstract: Networking unattended wireless sensors have significant impact on both military and non-military applications. Efficiency of wireless sensor network (WSN) depends on the correctness of the information those have been collected. At the same time, security is most important to prevent outsiders (i.e. illegitimate party) from retrieving the correct information. This paper proposes a user authentication mechanism to countermeasure the outside attacks. The salient feature of the proposed technique is that it establishes threshold number of session keys simultaneously between the user and individual sensor nodes during a single authentication process without using the public key cryptography. The proposed scheme therefore, reduces the computational complexity on one hand and enhances the security aspects on the other.

Abstract: The wireless sensor network is an emerging technology that may greatly aid humans by providing ubiquitous sensing, computing and communication capabilities, through which people can more closely interact with the environment wherever they go. To be context-aware, one of the central issues in sensor networks is location tracking, whose goal is to monitor the roaming path of a moving object. While similar to the location-update problem in PCS networks, this problem is more challenging in two senses: (1) there is neither a central control mechanism nor a backbone network in such an environment and (2) the wireless communication bandwidth is very limited. In this paper, we propose a novel protocol based on the mobile agent paradigm. Once a new object is detected, a mobile agent will be initiated to track the roaming path of the object. The agent is mobile since it will choose the sensor closest to the object to stay. The agent may invite some nearby slave sensors to cooperatively position the object and inhibit other irrelevant (i.e. farther) sensors from tracking the object. As a result, the communication and sensing overheads are greatly reduced. Our prototyping of the location-tracking mobile agent based on IEEE 802.11b NICs and our experimental experiences are also reported.

Abstract: Sensor networks deploy sensor nodes to detect and monitor environmental events and interactions. Existing sensor networks focus on communication within the bounds of resource restrained sensor nodes at the expense of security. In this paper, a review of sensor network components, architectures, algorithms and protocols aims to increase awareness of sensor network limitations and resulting strategies to ensure information security within wireless sensor networks. Because sensor networks deployments are increasing rapidly, designers and implementers need to be aware of attacks and best practices to reduce misuse and compromise of private information.

Abstract: Wireless sensor networks are being developed for use in monitoring a host of environmental characteristics across the area of deployment, such as light, temperature, sound, and many others. Localization plays an important role in wireless sensor network applications when the positions of nodes cannot be decided beforehand or, if nodes are mobile. A distributed, scalable algorithm for estimating the localization of nodes in a wireless sensor network is described in detail. Simulations were performed with the software of OMNeT++. The results show that in the presence of 5% measurement range errors, 20 percentages beacon node population, and average neighbors of 12 nodes, the estimation errors of the algorithm proposed are about 25% on average. It is also shown that, the algorithm performs well with up to 35% measurement range errors.

Proceedings of the 2nd ACM international workshop on Quality of service & security for wireless and mobile networks, pp. 51-54

inproceedings

Abstract: Real-time Digital Signal Processing (DSP) applications in wireless sensor network are often multi-rate in nature. These multi rate attributes provide additional significant opportunities in network design for achieving higher energy efficiency, besides traditional approaches of saving energy. In this paper, we propose a novel multi rate sensor network scheme to take advantage of power scaling for saving energy consumption. It can be easily synthesized into existing wireless sensor network MAC protocols, providing multi rate service for upper layer, and achieving communication energy efficiency. By monitoring a desirable BER threshold as the critical system parameter, the quality of received multi-rate data is assured. Based on this BER and the corresponding modulation scheme, the SNR at receiver end can be derived. The transmission power can be supplied optimally according to this SNR and the channel attenuation between sender and receiver. This dynamic power scaling scheme can lead to optimal energy efficiency since it demands that only a necessary amount of communication energy be consumed for multi-rate DSP applications. Our simulation shows that this multi data rate scheme with dynamic power scaling achieves energy saving significantly.

Abstract: Real-time Digital Signal Processing (DSP) applications in wireless sensor network are often multi-rate in nature. These multi rate attributes provide additional significant opportunities in network design for achieving higher energy efficiency, besides traditional approaches of saving energy. In this paper, we propose a novel multi rate sensor network scheme to take advantage of power scaling for saving energy consumption. It can be easily synthesized into existing wireless sensor network MAC protocols, providing multi rate service for upper layer, and achieving communication energy efficiency. By monitoring a desirable BER threshold as the critical system parameter, the quality of received multi-rate data is assured. Based on this BER and the corresponding modulation scheme, the SNR at receiver end can be derived. The transmission power can be supplied optimally according to this SNR and the channel attenuation between sender and receiver. This dynamic power scaling scheme can lead to optimal energy efficiency since it demands that only a necessary amount of communication energy be consumed for multi-rate DSP applications. Our simulation shows that this multi data rate scheme with dynamic power scaling achieves energy saving significantly.

Proceedings of the IEEE International Conference on Communications 2009 (ICC 2009)

inproceedings

Abstract: A widespread methodology for performance analysis in the field of communication systems engineering is network simulation. While ns-2 has established itself as virtually the standard network simulation tool, other network simulators have gained more and more attention during the last years. In this paper, we briefly survey new developments in the field of network simulation and conduct a performance comparison study by implementing an identical simulation set-up in five simulators, namely ns-2, OMNet++, ns-3, SimPy and JiST/SWANS. Our results reveal large differences according to both run-time performance and memory usage.

Proceedings of the 2003 International Symposium on Circuits and Systems (ISCAS '03)

inproceedings

Abstract: Continuing trends in sensor, semiconductor and communication systems technology (smaller, faster, cheaper) make feasible very dense networks of fixed and mobile wireless devices for use in many different sensing and decision-making systems. In this paper we present the design and development of GNOMES, a low-cost hardware and software testbed. This testbed was designed to explore the properties of heterogeneous wireless sensor networks, to test theory in sensor networks architecture, and be deployed in practical application environments. We also present an overview of architectures for extending the lifetime of individual nodes in the network, along with the design tradeoffs that this presents.

Abstract: IEEE 802.15.4 for Low-Rate Wireless Personal Area Networks (LR-WPANs) standard was designed specifically for simple, low-rate, and low power applications in Wireless Sensor Networks (WSNs). It is available in ns2 simulator and numerous commercial sensor motes. In this paper a comprehensive performance evaluation of IEEE 802.15.4 using ns2 and testbed experiments is presented. The purpose is to measure the performance of the standard in various settings and compare the results obtained from simulation and realistic experiments. The performance metrics include Throughput, Packet Delivery Ratio, and Delay.

Abstract: A wireless sensor/actuator network (WSAN) is a group of sensors and actuators that are geographically distributed and interconnected by wireless networks. Sensors gather information about the state of physical world. Actuators react to this information by performing appropriate actions. WSANs thus enable cyber systems to monitor and manipulate the behavior of the physical world. WSANs are growing at a tremendous pace, just like the exploding evolution of Internet. Supporting quality of service (QoS) will be of critical importance for pervasive WSANs that serve as the network infrastructure of diverse applications. To spark new research and development interests in this field, this paper examines and discusses the requirements, critical challenges, and open research issues on QoS management in WSANs. A brief overview of recent progress is given

Abstract: Wireless sensor networks have gained considerable attention in the past few years. In this article we present a WSN simulator - OMNET++. Through compare with some well-known simulator proves OMNET++ has better performance than NS2 and OPNET. We demonstrate the use of the WSN simulation by implementing Directed Diffusion protocols, and perform performance comparisons (in terms of the execution time incurred and memory usage) in simulating WSN in OMNET++ and NS2. The simulation study indicates the WSN in OMNET++ is much more scalable than NS2. It showed that OMNET++ is better than other simulator in large-scale WSN simulation.

Abstract: Wireless sensor networks have many applications, vary in size, and are deployed in a wide variety of areas. They are often deployed in potentially adverse or even hostile environment so that there are concerns on security issues in these networks. Sensor nodes used to form these networks are resource-constrained, which make security applications a challenging problem. Efficient key distribution and management mechanisms are needed besides lightweight ciphers. Many key establishment techniques have been designed to address the tradeoff between limited memory and security, but which scheme is the most effective is still debatable. In this paper, we provide a survey of key management schemes in wireless sensor networks. We notice that no key distribution technique is ideal to all the scenarios where sensor networks are used; therefore the techniques employed must depend upon the requirements of target applications and resources of each individual sensor network.

Abstract: Energy efficiency is one of the most important concerns in wireless networks because wireless clients usually have limited battery power. The aim of this work is to reduce energy consumption by exploiting multi-rate diversity in 802.11 wireless networks. An important observation is that ''probabilistic rate combination'' in transmission can significantly reduce power consumption. We formulate the energy efficient rate combination as a non-convex optimization problem. A non-cooperative rate adaptation scheme is presented to reduce power consumption without information exchange. Each node selects rate combination strategy and computes its transmission probability based on the weighted average interface queue length. Due to the well-known ''rate anomaly'' problem, selfish nodes may choose to transmit at a lower rate free ride from the other nodes. To mitigate this problem, we propose a joint consecutive packet transmission (CPT) and contention window adaptation mechanism (CWA). We prove the stability of our proposed algorithm, and to the best of our knowledge, this is the first control theoretical analysis on 802.11 ''multi-rate'' wireless networks. Simulation results show that the probabilistic rate combination can greatly save battery power, even up to 700% times compared with standard 802.11a/h protocol.

Proceedings of the Canadian Conference on Electrical and Computer Engineering (CCECE 2007), pp. 1372–1375

inproceedings

Abstract: Simulation for wireless sensor networks has become a challenging exercise due to the hardware design, energy constraints, and deployment of large number of nodes. NS-2 has been widely used in network simulations but does not perform well for wireless sensor networks. This paper provides a comprehensive analysis of the NS-2 simulator based on performance evaluation of simulation results, and proposes some improvements needed in NS-2 to cope up with wireless sensor network simulations.

Abstract: Wireless sensor networks (WSNs) have become an active research area for the researchers. The sensor nodes are generally unattended after their deployment in hazardous, hostile or remote areas. These nodes have to work with their limited and non replenish able energy resources. Energy efficiency is one of the main design objectives for these sensor networks. In this paper, we present the challenges in the design of the energy efficient medium access control (MAC) protocols for the wireless sensor network. We describe several MAC protocols for the WSNs emphasizing their strength and weakness wherever possible. Finally, we discuss the future research directions in the MAC protocol design.

Abstract: Node compromise poses severe security threats in wireless sensor networks. Unfortunately, existing security designs can address only a small, fixed threshold number of compromised nodes; the security protection completely breaks down when the threshold is exceeded. In this paper, we seek to overcome the threshold limitation and achieve resiliency against an increasing number of compromised nodes. To this end, we propose a novel location-based approach in which the secret keys are bound to geographic locations, and each node stores a few keys based on its own location. The location-binding property constrains the scope for which individual keys can be (mis)used, thus limiting the damages caused by a collection of compromised nodes. We illustrate this approach through the problem of report fabrication attacks, in which the compromised nodes forge non-existent events. We evaluate our design through extensive analysis, implementation and simulations, and demonstrate its graceful performance degradation in the presence of an increasing number of compromised nodes.

Abstract: This paper proposes S-MAC, a medium access control (MAC) protocol designed for wireless sensor networks. Wireless sensor networks use battery-operated computing and sensing devices. A network of these devices will collaborate for a common application such as environmental monitoring. We expect sensor networks to be deployed in an ad hoc fashion, with nodes remaining largely inactive for long time, but becoming suddenly active when something is detected. These characteristics of sensor networks and applications motivate a MAC that is different from traditional wireless MACs such as IEEE 802.11 in several ways: energy conservation and self-configuration are primary goals, while per-node fairness and latency are less important. S-MAC uses a few novel techniques to reduce energy consumption and support self-configuration. It enables low-duty-cycle operation in a multihop network. Nodes form virtual clusters based on common sleep schedules to reduce control overhead and enable traffic-adaptive wake-up. S-MAC uses in-channel signaling to avoid overhearing unnecessary traffic. Finally, S-MAC applies message passing to reduce contention latency for applications that require in-network data processing. The paper presents measurement results of S-MAC performance on a sample sensor node, the UC Berkeley Mote, and reveals fundamental tradeoffs on energy, latency and throughput. Results show that S-MAC obtains significant energy savings compared with an 802.11-like MAC without sleeping.

Abstract: Resource constraints in ad hoc wireless networks require that they are energy efficient during both transmission and rate adaptation. In this paper, we propose a novel energy-efficient rate adaptation protocol that selects modulation schemes online to maximize throughput based on channel state while saving energy. This protocol uses the distributed power control (DPC) algorithm (M. Zawodniok et al., 2004) to accurately determine the necessary transmission power and to reduce the energy consumption. Additionally, the transmission rate is altered using energy efficiency as a constraint to meet the required throughput, which is estimated with queue fill ratio. Moreover, back-off scheme is incorporated to prevent energy wastage and to avoid retransmissions in the event of congestion. The back-off scheme employs backpressure mechanism to emulate congestion control. Consequently, the nodes will conserve energy when the traffic is low, offer higher throughput when needed and save energy during congestion by limiting transmission.

Abstract: Rate adaptation is critical to the system performance of wireless networks. Typically, rate adaptation is considered as a MAC layer mechanism in IEEE 802.11. Most previous work relies only on frame losses to infer channel quality, but performs poorly if frame losses are mainly caused by interference. Recently SNR- based rate adaptation schemes have been proposed, but most of them have not been studied in a real environment. In this paper, we first conduct a systematic measurement-based study to confirm that in general SNR is a good prediction tool for channel quality, and identify two key challenges for this to be used in practice: (1) The SNR measures in hardware are often uncalibrated, and thus the SNR thresholds are hardware dependent. (2) The direct prediction from SNR to frame delivery ratio (FDR) is often over optimistic under interference conditions. Based on these observations, we present a novel practical SNR- Guided Rate Adaptation (SGRA) scheme. We implement and evaluate SGRA in a real test-bed and compare it with other three algorithms: ARF, RRAA and HRC. Our results show that SGRA outperforms the other three algorithms in all cases we have tested.

Abstract: Originally designed to deal with the hidden node problem, the Request-to-Send/Clear-to-Send (RTS/CTS) exchange is often turned off in most infrastructure-based 802.11 networks with the belief that the benefit it brings might not even be able to pay off its transmission overhead. While this is often true for networks using fixed transmission rate, our investigation leads to the opposite conclusion when multiple transmission rates are exploited in WLANs. Through extensive simulations using realistic channel propagation and reception models, we found out that in a heavily loaded multi-rate WLAN, a situation that we call rate avalanche often happens if RTS/CTS is turned off: high collision rates not only lead to retransmissions but also drive the nodes to switch to lower date rates; the retransmissions and the longer channel occupation caused by lower rates will further deteriorate the channel contention, which yields more collisions. This vicious circle could significantly degrade the network performance even no hidden node presents. Our investigation also reveals that, in the absence of effective and practical loss differentiation mechanisms, simply turning on the RTS/CTS could effectively suppress the rate avalanche effect. Various scenarios/conditions are extensively examined to study the impact of RTS/CTS on the network performance. Our study provides some important insights about using the RTS/CTS exchange in multi-rate 802.11 WLANs.

Abstract: In-network processing presents a critical challenge for data authentication in wireless sensor networks (WSNs). Current schemes relying on Message Authentication Code (MAC) cannot provide natural support for this operation since even a slight modification to the data invalidates the MAC. Although some recent works propose using privacy homomorphism to support in-network processing, they can only work for some specific query-based aggregation functions, e.g. SUM, average, etc. In this paper, based on digital watermarking, we propose an end-to-end, statistical approach for data authentication that provides inherent support for in-network processing. In this scheme, authentication information is modulated as watermark and superposed on the sensory data at the sensor nodes. The watermarked data can be aggregated by the intermediate nodes without incurring any en route checking. Upon reception of the sensory data, the data sink is able to authenticate the data by validating the watermark, thereby detecting whether the data has been illegitimately altered. In this way, the aggregation–survivable authentication information is only added at the sources and checked by the data sink, without any involvement of intermediate nodes. Furthermore, the simple operation of watermark embedding and complex operation of watermark detection provide a natural solution of function partitioning between the resource limited sensor nodes and the resource abundant data sink. In addition, the watermark can be embedded in both spatial and temporal domains to provide the flexibility between the detection time and detection granularity. The simulation results show that the proposed scheme can successfully authenticate the sensory data with high confidence.

Abstract: The significant advances of hardware manufacturing technology and the development of efficient software algorithms make technically and economically feasible a network composed of numerous, small, low-cost sensors using wireless communications, that is, a wireless sensor network. WSNs have attracted intensive interest from both academia and industry due to their wide application in civil and military scenarios. In hostile scenarios, it is very important to protect WSNs from malicious attacks. Due to various resource limitations and the salient features of a wireless sensor network, the security design for such networks is significantly challenging. In this article, we present a comprehensive survey of WSN security issues that were investigated by researchers in recent years and that shed light on future directions for WSN security.

Abstract: Nodes in most wireless sensor networks (WSNs) are powered by batteries with limited energy. Prolonging network lifetime and saving energy are two critical issues for WSNs. Some energy-saving routing algorithms like minimum spanning tree based ones can reduce total energy consumption of a WSN, but they place too heavy burden of forwarding data packets on several key nodes so that these nodes quickly drain out available battery energy, making network lifetime shortened. In this paper, a routing algorithm termed Energy-efficient Routing Algorithm to Prolong Lifetime (ERAPL) is proposed, which is able to dramatically prolong network lifetime while efficiently expends energy. In the ERAPL, a data gathering sequence (DGS), used to avoid mutual transmission and loop transmission among nodes, is constructed, and each node proportionally transmits traffic to the links confined in the DGS. In addition, a mathematical programming model, in which minimal remaining energy of nodes and total energy consumption are included, is presented to optimize network lifetime. Moreover, genetic algorithms are used to find the optimal solution of the proposed programming problem. Further, simulation experiments are conducted to compare the ERAPL with some well-known routing algorithms and simulation results show the ERAPL outperforms them in terms of network lifetime.

Abstract: Recent work in sensor network energy optimization has shown that batch-and-send networks can significantly reduce network energy consumption. Batch-and-send networks rely on effective batch data transport protocols, but the throughput of state-of-the-art protocols is low. We present conditional immediate transmission, a novel packet forwarding mechanism, with which we achieve a 109 kbit/s raw data throughput over a 6-hop multi-channel 250 kbit/s 802.15.4 network; 97% of the theoretical upper bound. We show that packet copying is the bottleneck in high-throughput packet forwarding and that by moving packet copying off the critical path, we nearly double the end-to-end throughput. Our results can be seen as an upper bound on the achievable throughput over a single-route, multi-channel, multi-hop 802.15.4 network. While it might be possible to slightly improve our performance, we are sufficiently close to the theoretical upper bound for such work to be of limited value. Rather, our results suggests that other mechanisms, such as multi-route forwarding, may be fruitful way to further improve multi-hop throughput.

Abstract: This document aims to highlight the issues affecting co-existence of IEEE 802.15.4 or ZigBee systems in the presence of interference. The measures employed by the 802.15.4 standard to ensure reliable co-existence are outlined. The practical performance of IEEE 802.15.4/ZigBee systems are established with reference to supporting empirical and simulated data. Finally, guidelines are provided for installing sensor networks in either a planned or unplanned RF environment.